Fibrous glass wool or board insulating materials and acoustic panels, and similar products fabricated from fibers of other composition, such as mineral or basalt fibers, are typically produced by deposition of the fibers from entrainment in at least one stream of gas as those gas streams pass into a fiber deposition zone, which ordinarily is bounded from below by a porous support moving along the base of a region surrounding and separating the fiber-entraining gas streams which pass through it toward the porous support, the transverse boundaries of this region ordinarily being defined by a pair of generally vertical walls. Typically the fibers are produced by the expression of streams of liquid, e.g. molten, fiber-forming material such as glass through orifices in a suitable container supplied with the liquid fiber-forming material, as by centrifugal expression from a generally bowl-shaped container having suitable perforations in its sidewalls into a generally axial stream of gas, usually a confluence of hot gas flowing from a generally axially directed gas burner jet augmented with air supplied from a blower, for attenuating the emerging streams of liquid fiber-forming material and entraining the fibers so formed. Ordinarily the fiber attenuating and entraining gas streams will be comprised of hot gas and will pass through a region of substantially cooler gas into the fiber deposition zone.
A resinous binder is frequently incorporated in the fibrous product, typically by spraying a solution or emulsion thereof or of a precursor thereof, into the fiber-entraining streams of hot gas wherein the solvent or dispersing medium is volatilized and the binder or its precursor is deposited onto the fibers and carried by them into the mass of entangled fibers as it forms in the deposition zone. Thereafter the binder or its precursor may be cured or otherwise reacted by exposing the entangled fibrous mass to heat, radiation, etc., and the entangled fibrous material may be trimmed, slit and/or cut to desired dimensions and may be laminated to other substrates and/or facings.
Such binder compositions frequently also contain a dust suppressant such as petroleum brightstock or tempering oil to suppress the evolution of dust from the product, primarily during handling and installation. However, such dust suppressants are found to contribute to pollution of the effluent gas from the deposition zone and of the surrounding workplace, and also of the effluent and surroundings of any downstream oven in which the fibrous mass may be heated to cure the binder therein, as evidenced by reduced light transmittance indicating increased smoke generation as the amount of such dust suppressant applied as part of the binder composition is increased. Such a process, and suitable apparatus therefor, is described in detail in U.S. Pat. No. 3,523,774 of Aug. 11, 1970 entitled Rotary Apparatus for Forming Glass Fibers, incorporated herewith by reference.
The present invention reduces such increased smoke evolution, at least in the fiber entrainment and deposition stages, by providing a method for incorporating at least a portion of the dust suppressant otherwise than by introducing it into the hot gas streams in which the fibers are entrained prior to their deposition. This method also reduces the waste of dust suppressant by reducing the amount converted to smoke.